ESTRO 2025 - Abstract Book

S1764

Clinical – Upper GI

ESTRO 2025

each organ-at-risk as the mandatory constraint, and the lower quartile as the optimal constraint, which were then scaled for the 40.05Gy/15# prescription. The scaled constraints were then subject to clinical review by two of the PROTIEUS RTTQA reviewers, before being tested on a representative case by four UK centres who had participated in SCOPE 2, to create the final agreed objectives used for PROTIEUS.

Results:

The table shows the development of the final dose constraints. The proposed objectives were revised after clinical review to be more realistic for a multi-centre trial. These final objectives were met by all four centres, without adversely affecting PTV coverage. Conclusion: The SCOPE 2 planning data has shown that photon OAR dose constraints for oesophageal cancer can be tightened further, with potential to reduce the incidence and severity of toxicities associated with RT. This is of particular relevance to a trial comparing photons and protons with post-operative toxicity as an endpoint. These lower OAR dose constraints have been included in the PROTIEUS trial planning guidance, but by retaining the use of optimal and mandatory objectives, we hope to allow for complex or difficult cases to be included in the trial. This will maximise trial recruitment and maintain patient access to novel treatment modalities. The on-trial QA component of PROTIEUS will allow us to assess how well centres are meeting these new constraints, allowing further modification if required.

Keywords: Clinical Trials, Oesophageal Radiotherapy, Protons

References: Crosby et. al (2020) SCOPE2 Radiotherapy Planning Guidance Document v3.0. Cardiff: Velindre University NHS Trust Radhakrishna et. al (2024) PROTIEUS Radiotherapy Planning Guidance Document v1.2. London: University College London